that stuff is connective tissue. It isn't fat, and it isn't carbohydrate, so it only be beef protein. Your stomach acids have no trouble digesting it and passing it on to your bloodstream for use.
I myself, spit most of it out after chewing the melts-in-your-mouth fat out, as I try to restrict the amount of protein I eat.
If you have enough ambition, you can learn to trim it out of your rations, as it actually is NOT identical in appearance to true fat. It is present in the form of sheets, same as the fascia in your own mammal body. Commercial butchers don't, simply because they are ruled by time contraints. You may not be.